Along with rapid development of a mobile communication technology, broadband wireless communications becomes a predominant development trend of future mobile communications. The International Telecommunication Union (ITU) has further provided a more powerful and advanced mobile communication system, i.e., IMT-Advanced, based upon the International Mobile Telecommunications-2000 (IMT-2000). The IMT-Advanced system with the maximum wireless communication bandwidth up to 100 MHz supports low-level to high-level mobility applications and data rates in a very wide range. In the IMT-Advanced system, the maximum transmission rate may be up to 1 Gbps to satisfy demands of a user and a service in various user scenarios, for example, the user may enjoy numerous wireless mobile services such as high-speed data downloading, Internet shopping, mobile video chatting, and a mobile phone television, thereby enriching greatly the life of the user. The IMT-Advanced system is further capable of offering a high-quality multimedia application with a significantly improved Quality of Service (QoS).
In an existing 3GPP Long Term Evolution (LTE) system, uplink data and control signaling of a broadband wireless communication system is transmitted in an approach of a signal carrier for the purpose of reducing a Peak-Average Power Ratio (PAPR) of the uplink signal and hence improving coverage of the uplink signal. At present in the LTE system, Discrete Fourier Transform-Spread Orthogonal Frequency Division Multiplexing (DFT-S OFDM), similar to the Orthogonal Frequency Division Multiple Access (OFDMA) adopted in an approach of generating a signal, is adopted in an approach of an uplink signal carrier. Specifically, an approach of generating a signal over the DFT-S OFDM is as illustrated in FIG. 1.
At a transmitter, firstly signal data for transmission is modulated and a data stream for transmission is segmented, then the segmented data stream is serial-parallel (S/P) converted, and next the serial-parallel converted data is transformed in a Discrete Fourier Transform (DFT) process to the frequency domain where it is further spread and subject to an Inverse Fast Fourier Transform (IFFT) process and finally appended with Cyclic Prefixes (CPs) to generate a random sequence in the time domain. A serial-parallel converted data block is assumed as s={s1, s2, . . . , sM}, and the random sequence generated from the DFT and IFFT processes is assumed as s={s′1, s′2, . . . , s′N}. Correspondingly at a receiver, a high-rate data stream is parallel-serial converted over the DFT-S OFDM so that duration of a data symbol over each sub-carrier is relatively increased to thereby reduce effectively both inter-symbol interference due to temporal diffusion of a wireless channel and complexity of balance in the receiver. Balance in the frequency domain may facilitate processing of the signal at the receiver.
In FIG. 1, in order to ensure a process of balancing a signal in the frequency domain and reduce complexity of implementing a system, the signal is processed over the DFT-S OFDM like a downlink Orthogonal Frequency Division Multiplexing (OFDM) symbol, so that users may be distinguished from one another over the Frequency Division Multiple Access (FDMA) where different sub-bands are occupied to thereby enable a multiple access of the users. Unfortunately, the DFT-S OFDM multiple access still has the following drawbacks.
In an application of the uplink DFT-S OFDM multiple access to a cellular mobile communication system, networking at the same frequency may result in significant inter-cell interference because users in different cells with reception and transmission of data over the same sub-carrier may possibly interfere reception and transmission of data of a user terminal in an adjacent cell. Especially at an edge of a cell, a user terminal at a relatively short distance from another cell is subject to a relatively strong signal arriving from the other cell, and during reception and transmission of data at the user terminal, serious mutual interference may arise between signals of the adjacent cells, so that communication performance of the user terminal at the edge of the cell may be degraded sharply.
In order to avoid interference of a signal from an adjacent cell in the case of networking at the same frequency, a relevant modified solution has been proposed, for example, interference of a signal in the case of networking at the same frequency may be reduced by combining the Code Division Multiplex Access (CDMA) and the OFDM in downlink OFDM modulation. At present, the multiplex access in which the CDMA and the OFDM are combined typically includes the Multi-Carrier CDMA (MC-CDMA), the Multi-Carrier-Direct Spreading-CDMA (MC-DS-CDMA) and the OFCDMA in which two-dimension spreading in the time and frequency domains and the OFDM are combined.
Particularly, an approach of generating a signal over the MC-CDMA is as illustrated in FIG. 2, the flow of which is as follows: firstly each of several data symbols in a data stream consisted of the symbols is spread, and then the spread data is mapped onto OFDM modulated sub-carriers over which the spread data symbols are output. The length of a spreading code is assumed as N, and then the spread data is mapped onto a number N of sub-carriers f1, f2 . . . fN. The MC-CDMA has advantages over the OFDM of utilizing frequency diversity and reducing interference between adjacent cells in the case of networking at the same frequency.
An approach of generating a signal over the MC-DS-CDMA is as illustrated in FIG. 3, the flow of which is as follows: firstly a data stream consisted of several data symbols is serial-parallel converted and the data is mapped onto various sub-carriers, then each symbol is spread over the corresponding sub-carrier, i.e., spread temporally, to achieve a gain of temporal diversity, and thereafter the spread data symbols are output. The length of a spreading code is assumed as N, and a number N of sub-carriers are f1, f2 . . . fN. The MC-DS-CDMA also has an advantage over the OFDM of reducing interference between adjacent cells in the case of networking at the same frequency.
Further to the foregoing two multiple access approaches in which the CDMA and the OFDM are combined, there is also the Orthogonal Frequency and Code Division Multiplexing (OFCDM) in which two-dimension spreading in the time and frequency domains and the OFDM are combined, where each data symbol is spread temporally by a factor of M and also spread by a factor N over a sub-carrier, as illustrated in FIG. 4, by a factor of 4 in the time domain and 2 in the frequency domain.
The above solutions of MC-CDMA, MC-DS-CDMA and OFCDM in which the CDMA and the OFDM are combined may also be applicable to an approach of generating an uplink DFT-S OFDM signal. These solutions may all achieve specific gains of diversity and an anti multiple access interference capacity, easily achieve networking of plural cells at the same frequency and reduce interference between the adjacent cells in the case of networking at the same frequency. Like the CDMA, however, the foregoing solutions are demanding for temporal and frequency synchronization of a signal, where the same time and frequency resources have to be occupied for data of the cells to detect signals of users of the cells, thus requiring coordination and scheduling of the resources between the cells. Moreover, detection for the users also necessitates information available to the UE about time and frequency resources and spreading codes occupied by other users. In the foregoing several solutions, neither allocation and scheduling of resources nor coordinated control of interference is sufficiently flexible and convenient; multiple access interference has to be eliminated at the receiver in a complicated process at a high cost; and channel fading and interference may also give rise to a sudden error of some symbols.